Process of using normally gaseous solvents to separate wax and oil



July 25, 1944. E. M. DONS ETAI.

' PROCESS USING NORMALLY GASEOUS SOLVENTS TO vSEPARATE WAX AND OIL Filed March 2, 1942 INVENToR; E. M. DONS O. G. MAURO AT TOR N EYS. y

Patented July 25, 1944 lPROCESS F USING NORMA-LLY lG'rASEOUS 'SOLVENTS T0 SEPARATEWAX ANDOIL Eddie M. Donsv and Oswald G. Mauro, Tulsa, n

Okla., assignors to Mid-Continent Petroleum Corporation, Tulsa, Okla., a corporation Yof Delaware Application March ,2, 1942,- ,seriai No. 432,963 (ci. 19e-1s) 3 Claims.'

This invention relates lto processes of using :normally gaseous solvents to separate waxand oil. The invention may be employed in separating Wax and oil found in various kinds of materials including mineral oils, petrolatum and slack wax. It can be conveniently used in dewaxing petroleum lubricating oils to produce low pour point lubricants.

The main object of the invention is to lproduce a relatively simple and inexpensive method of using normally gaseous dewaxing solvents `lacking several serious objections `found in priory processes. The commercial development of dewaxing systems has passed through a series of stages, which eventually led to the modernv dewaxing systems wherein extremely large lters are employed to separate wax from diluted oil.

Nevertheless, the highly developed conventiona filtering processes now in general use are complex systems, involving considerable trouble and expense, and lacking .the desired efliciency in the separation of waxgfrom oil. In commercial practice, clusters of wax crystals are deposited on the lters with portions of the oilsolution trapped or occluded in the wax clusters.v The filtration does not remove this occluded oil solution from the wax clusters, and additional portions of the solution are trapped between the clusters on the lter. v

A primary object of the invention is to advance this art by producing a very simple and .inexpensive commercial system, lacking inherent defects, or objections, found in the dewaxing systems which have been generally adopted in this industry. y

A specific object of the present invention is to produce an entirely feasible dewaxing system wherein normally gaseous dewaxing solvents areA deliberately employed to forcibly disintegrate the wax. We realize that experts in this art have regarded even a slight or incidental disintegration of the wax as a nuisance or objectionable condition to be carefully avoided in the separation of wax and oil. However, a study of the plan herein set forth will show that wefhave established novel conditions wherein this radical departure from the usual practice is employed to obtain substantial advantages. -f

Instead of exercising precautions to avoidv a possibility of slight disintegration, we have created cooperative conditions wherein rather severe disintegrationl of the wax is an outstanding factor tending to promote separation of the wax and oil.

For example, propane is a very popular normally gaseous solvent having special advantages for dewaxing, including the intense chilling which occurs when propane is evaporated in the oil solution. However, in commercial practice special precautions are exercised to avoid a sudden expansion which would rupture the precipitated wax clusters, or otherwise result in disintegration of the wax. This usual commercial practice has resulted in so called critical rates of chilling, requiring gradual evaporation of propane, intended to avoid shock chilling which would rupture the wax `clusters,qor Iotherwise interfere with the usual methods vof separating the wax from the propane solution. vIn this popular commercial procedure, the freev oil solution is transmitted through a `iilter, while substantial portions of the solution are trapped, or occluded, in the wax cake deposited on the filter.

To overcomethese problems, we will show how the wax can be deliberately subjected to a forcible*l disintegrating operation, which liberates practically all of the oil solution from the wax; This-maybe regarded as Va desirable-preliminary step in the new sequence of operations wherein the departure from conventional theories is employed to improve the art of using normally gaseous dewaxing solvents.

A special advantage is gained by suddenly' evaporating portions of the normally gaseous material in the precipitated wax, as this will result in a sudden explosive forcewhich forcibly disintegrates the wax, thereby positively kreleasing oil solution which is usually trapped inthe wax.v The liberated oil solution will thenbe free to separate from the wax in the dewaxing or deoiling operation. This is a substantial advantage -over the usual commercial practice, wherein trapped or occluded oil is inevitably retained within and between wax clusters deposited on the filters. K f v A separate and distinct object of thepresent invention is to obtain advantages of using a nor-` mally gaseous solvent, including the advantage of evaporating portions of the solvent to produce the desired degree of chilling, and at the same time avoid the usual trouble, expense and ineiciency involved in the ordinary ltering plants. This phase of the invention may be advantageously employed in the sequence of operations which include forcible disintegration-of the wax, but it has special advantages which may be gained without subjecting thewax to said forcible disintegration.v

, `Briefly stated, the liqueed normally gaseous solventvmay be mixed with the wax-,containing of dewaxed solution may be= discharged from an' upper portion of the settling chamber, thereby dewaxing a 'major portion of the oilsolutio'n. A descending stream of Wax with portions of the oil solution is preferably discharged from a lower portion of the settling chamber to a counterflow deoiling system, Where the wax issubjected to a deoiling operation and then dischargedY from the system.

The deoiling operation may be performed by transmitting a rising stream of liqueed normally gaseous solvent through a descending stream' of wax, so as to dissolve oil solution carried by the wax, and we will hereafter show how a stream of the used deoiling solvent, with the oil solution dissolved therein, may be transmitted to the Waxcontaining charging stock, so as to recycle the dissolvedoil from the deoiling system, and at the same time utilize the deoiling solvent in forming the dewaxing solution.

With the foregoing and other objects in view, the'invention comprises a novel sequence of operations hereinafter more specifically described and shown in the accompanying drawing to illustrate one form of the invention. However, it is to be understood that the invention comprehends changes, variations'and modiiications within the scope of the claims hereunto appended.

The accompanying drawing is a diagrammatical view of a system which may be employed to carry out one form of the invention.

A continuous regulated stream of the waxbearing charging stock, for example, a lubricating oil stock, enters the system through a pipe I which may be provided with a pump 2 and a regulating valve 3. A continuous stream of liqueed normally gaseous dewaxing solvent, from sources to be hereafter described, is conducted through a pipe 4 to the oil supply pipe I. The continuous streams of oil `and dewaxing solvent areunited in the pipe I and transmitted through a mixing nozzle 5 where the oil and solvent are mixed at a temperature high enough to form the desired solution.

The continuous stream of solution from the mixer 5 passes through a heat exchanger 6 to a pipe 1 leading to an insulated chamber'8, said pipe 'I being equipped with a pressure-reducing valve 9 to provide fora reduction in the pressure of the stream entering the chamber 8. The valve 8 is adjusted to provide for evaporation of portions of the normally gaseous solvent, thereby chilling the remaining oil solution to precipitate Wax therein.

Any suitable normally gaseous dewaxing solvents may be employed in this system. Examples appear in propane, methane, ethane, and mixtures including these relatively light hydrocarbons. However, for convenience in describing the invention, We will refer to propane as a suitable normally gaseous solvent, without limiting the invention to this specic solvent.

To provide the desired ratio of solvent in oil to be dewaxed, a regulated stream of cold liquid propane may be transmitted through a pipe I Il to the pipe 1, said pipe I'U being equipped with a pump II and regulating valve I2. An advantage can be gained by introducing the propane from pipe I0 in a very cold condition, for example, at a temperature lower than about 40 F., so as to suddenly chill the relatively warm solution to a temperature of about 10 F. More specifically stated, the incoming solution may pass from the heat exchanger 6 at a temperature of about 60 F., and the shock chilling due to the stream from pipe IU may suddenly chill the oil solution to a temperatureof about 10 F., thereby instantly precipitating .high melting point waxes. This preliminary chilling also reduces the chilling requirements in the chamber 8. However, in commercial practice, the chamber 8 may be relatively large to provide the desired capacity, and a series of such chambers may be employed, instead of using a single chamber 8.

Instead of adhering to the generally accepted critical rate ofvery gradual chilling, we preferably regulate the valve 9 to very suddenly reduce the pressure in a disintegrating zone formed by the chamber 8. An instantaneous reduction of this pressure will result in sudden evaporation of portions of the solvent, so as to suddenly chill and precipitate wax fractions in a liquid solution of the oil and solvent. Furthermore, this violent ash chilling will suddenly expand the evaporating portions of the solvent to produce an explosive effect, thereby forcibly disintegrating the wax. The oil solution is thus liberated from the wax, and there is no opportunity for the usual formation of wax clusters which occlude or trap portions of the oil solution in the wax.

Of course, this violent disintegration may not produce readily iilterable wax. However, one of the objects ofthe invention is to dewax the oil without resorting to trouble and expense of employing the conventional lter plants, and as a preliminary step, we preferably disintegrate the wax to liberate all of the oil solution for the dewaxing operation.

The disintegrating chamber 8 is provided with a gas outlet pipe I3 at the top, and a valve I4 in said pipemay be regulated to control the discharge of gas. Any suitable recovery system may be employed to liquefy this gas for reuse in the system.

We will now refer to a settling chamber, or dewaxing chamber, I5 surrounded by the upper portion of an insulated column I6. An annular space may be formed around said settling chamber I5 to provide an outer settling chamber I 'I to be hereinafter described. The chamber I5 may be open at the bottom to form a Wax outlet I9, and the top of said chamber I5 may be provided with a pipe 20 having a valve 2I to regulate the discharge of dewaxed solution.

A continuous stream of disintegrated wax and oil solution is discharged from the bottom of the chamber 8, through a pipe 22 leading into the dewaxing chamber I5 as shown in the drawing. This pipe 22 is equipped with a pump 23 and valve 24 to regulate the flow of Wax and oil solution to the dewaxing chamber I5. The incoming stream of cooled solution and wax may be delivered to this chamber at approximately the temperature selected for precipitation of wax in the disintegrating chamber 8. For example, in using propane to dewax lubricating oils, this temperature may be about 40 F., although higher and lower temperatures may be employed in separating various kinds of waxy materials.

We are now assuming that a relatively light solvent has been selected for the dewaxing operation in the chamber I5, and that the viscosity` and interfacial tension are low enough to allow the wax particles to descend in the relatively light solution. In this event, the major portion of the light solution will rise to the top of the dewaxing chamber I5, where it is discharged in the form of a continuous stream through the pipe 20. This outgoing solution is free of wax, and it may be distilled in any suitable manner to remove the solvent from the dewaxed oil.

,Attention is. i now directed .to the; separating.

zone, or dewaxingzonaestablished nearthe pointv where the incoming mixture of cooled solution"- and wax begins to separate in the chamber' l5. The disintegrated wax particles move downwardf 1y and carry with themportions of the koil solution, including oily films and relatively free portions of the solution between the descendingwax particles.l 'I'he major'portion of the light oil'solu` tion freely rises to thetop of the chamber l5, but @minor portion of this oil solution isv carried downwardly `with the wax, vwhich is discharged'y vfrom a lower portion offsaid chamber I5'.- l

:,Therefoie, as asupplement tothe dewaxingoperationv herein claimed, advantages can be gained iby subjecting this outgoing vwax to a. simple deoiling operation. For4 example, thewax may be ltransmitted through a counterflowingstream of selective oil ysolvent to dissolve and cover oil solution carriedby the wax.

-To illustrate a suitable condition of this kind,

refr. 1 20 we have shown a counterflow deoiling system ini-.f cluding the insulated column l5 associated with`vr the dewaxing chamber I5.

The mass of -wax .descending from. the chame fber l5 passes 'through arelatively light rising'. stream which may be produced-by continuously introducing a stream :of deoiling solvent throughv a pipe 25 leading into the lower portion of the column i6. The pipe 25 is` equipped with a pump 26and a regulating valve 2l'adjusted toregulate the ow of the incoming deoiling solvent. The stream of deoiling solvent from. thepipe 25 Will ris'e in direct lContact with vthe descending stream of wax particles, so as toV selectively' dissolve the freeportions vof oil .solution 'carried by the wax, and also forcibly scrub. thev oily lms from the descending wax particles. This action may be v cic gravities contacting with each other and adv-z vancing inintersectingpaths as they flow from These baffles vareprefer` ably pro-vided witli'downwardly inclined top and'v one baille to another.

bottom faces to permit free movement of the descending wax particles. lIt will lbe observed that the descendingl layers of Wax particles move downwardly while in contact with the downwardly inclined top faces of the ibale's, and that said wax' particles repeatedlyl intersect the-rising solvent while descending from one'inclined plane to ari-v other; A continuous stream `of deoiled wax withy a minor portion of the solvent may be discharged through a pipe 3B Vb'elowfthe inlet for the deoiling solvent.

-The inclined faces of the lbaliles However, any suitable mechanical means may be employed to prevent or limit the growing of wax crystals which might 'otherwise extend from the top faces of the baiiles. For example, the central baffles 29 may be fixed to a slowly rotating shaft 3l so as to rotate with the shaft, and Scrapers 32 may extend fromvbottom faces of these rotary baffles may be ylikewise provided with scrapersf 33 extending fromv their bottom faces to remove waxy material from'the top faces of the' rotatingv baffles. kAn, interesting condition yappears in the effec# tivecleansing of the descending wax particles due"v to the forcible scrubbing and dissolving action.; f. of theA selective deoiling solvent which repeatedly.'

crosses thepath of the wax inthe deoiling zon'e' Attention is alsodirected .to the condition atthe upper portionV of this deoiling zone where'. the rise.A

ing solvent ystream is diverted'from the interior of the dewaxing chamberL l5. This deflection ofv`r the rising solvent is due partly to the .downwardf force of the descending-'streamv Yofv Wax particles-v` issuing from l. the ibottom' of .said chamber'- I5; and partly to arising current in the'surroundin'g'l chamber or passagewayyll. The highest centrali' baffle 29 alsotends to deflect the rising solvent Atdi" Ward the'chamber Il.' Some of thewaxparticle's? 'may beswept into the settlingy chamber lljfbut these Wax particles are relatively heavy `so they willeventually fall in the'flighter solvent and return to lthernass of'wax, .instead of` passing to the top of said settling chamber' l1. vf

The selective deoiling-solvent performs avery important `function in. 'selectively removing o'i* carried .by the wax particles. However, most'offy the oil' is removed from the waxin the dewaxing chambergi 5, so the deoiling solvent streamwhich rises through the settling compartment Il con-2 tains a relatively small percentage of the original oil. Therefore, this reasonably fresh fbody" of i. f selective oil solvent can be veryconveniently used.'

in thefdewaxing stage of. the process.. Fori-"exa" ample,;it may becontinuously transmitted' from' Athe-top of the y.settling compartment Il through a pipe 34 and through a pump 35 and valve'iy inf saidpipe 311 which leads to the heat exchanger B, :and thence through pipe 4Lto the continuous incoming `stream of wax-bearing oil inthe pipe-1.1

The velocityand time of the deoilingaction"l maybe regulated to .dissolve practically all ofthe oil carried by the Wax, or any desired :percentage upon the commercial requirements. y

It is ,to beunderstood that the invention is vnot limited to the specific arrangements of chambers and zones herein disclosed to illustrate one'forrr'i` of the invention, and that anyfsuitable solvents of oil may be discharged with the wax, depending may be employed to produce the counterflow of- Wax and solvent in the deoiling system. How-` v 'on tend to prevent the wax vparticles fromv clinging to said baiiles.V

bailes to remove waxy material from the tops of 76 ever, when the deoiling solvent admitted through thepipe 25 is eventually transmitted to thek in comingcharge in the pipe` Liso as to serveas a dewaxing solvent, an advantage may ibe gained by selecting a solvent suitable for both operations.

For example, if the primary dewaxing solvent is." propane, a stream .of fresh cold propane.. inra" liquid state' maybe admitted through thepipe 25, `and after performing its deoilingfunction inY the counterflow system, this liquid propanean'd4 the oily dissolved therein, may be transmitted through the pipes 34 and 4 to the incoming stream= of charging'stock in the pipe i. kThe oil recovered' in .theideoiling operation is thus veryleconomically recycled to .the charging stock, while the Aused' deoiling solvent is employed as a dewaxing operation.

. 'Thisv procedure enables a single solventfto very4 effectively perform two successive functions, While recycling recovered oil to the incoming charge. It also eliminates la distillingoperation which would otherwise be required to separate the dethe stationary :baffle rings 28. These ystationary-fsolvent" for fthe oiling solvent from its recovered oil, and if any` of the valuable fwax should be incidentally dissolved in the deoiling solvent, such wax will bey recycled to the' incoming charging stock.

The term disintegrating as used in' `the claims refers to the eiect o-f sudden expansion which forcibly separates a crowded mass of wax particles; In some cases, portions of the solvent may be securely trapped, or occluded, in relatively large clusters of the wax particles', so as to provide an internal bursting force when the pressure is Y suddenly reduced. In vother cases, the' "disintegrating eiectoccurs in a crowded mass of individual Wax crystals before they'have an opportunity to unite. in 4the form of relatively large wax clusters. -For example', an intense flash chilling at the chamber 8 will produce a crowded mass of elementary wax crystals, but the ,-fdisintegrating eiect of the sudden expansion will forcibly disintegrate or scatter this crowded mass, so as to avoid the usualtrapping ofoil solution in the precipitatedwax.

We claim:

1. In the art of using normally gaseous selective dewaxing solvents .to chill oilsolutions to de-y waxing temperatures, the process of dewaxing oil and deoiling the wax which comprises .mixing a wax-containing oil with liqueed normally gas-A eous dewaxing solvent under pressure, to form adewaxing solution, reducing the pressure to evaporate portions of the solvent, thereby chilling the remaining-oil solution .to precipitate wax therein, transmitting a mixture of the wax and oil solution into a settling chamber, discharging a; stream of dewaxed oil solution from an upper portion of said settling chamber, discharging a stream of Wax with portions of the oil solution diverting the last mentioned stream from the contents of saidsettling chamber, and transmit-` ting said last mentionedstream of liquefied normally gaseous Solvent and dissolved oil solution' to said Wax-containing. oil, so as to recycle theI dissolved oil from said deoiling system and at the same time utilize the last mentioned solvent in forming said dewaxing solution.

v2.'In the art ofusing normally gaseous selectivel dewaxing solvents to chill oil solutions to dewaxing temperatures, the process of dewaxing.v

oil and deoiling the wax which comprises mixing a `wax-containing oil with liqueed normally gaseous dewaxing solvent under pressure to form a' dewaxing solution, reducing the pressure to evaporate portions of thev solvent,fthereby chillingthe remaining oil solution to precipitate wax therein, transmitting a mixture of the wax and oil solution into a settling chamber, discharging a stream of dexawed loil solution from an upper portion of said settling chamber, discharging a. stream Lof wax with portions of the oil solution fromialower portion of said settling chamber to a counterflow deoiling-system, transmitting a ris-- ing stream of liquefied normally-gaseous solvent througha 'descending lstream of Wax in said de# oiling system, dividing the risingr and descending streams :into numerousl layers 4of dierent Aspe"- cific gravities :contacting with each other at different elevations'in said 'deoiling system, causing the counterowing streams of'wax and solvent'tof flow in intersecting paths While-moving from onel of said elevations to another, so -fas'to forcibly scrub oil solutionl from the 'Waxjdischa'rging dei' oiled waxlf from a lower 'portion ofsaidl deoiling system, discharging'a stream of the used solvent with its dissolved oil solution from an upper portion of said deoiling system while'diverting the last mentioned stream from the contents of said' settling chamber, and transmitting said last mentioned stream of lqueed normally gaseoussolvent and dissolved oil solution to said waxcontaining oil, so as to recover said oil solution and at the same time utilize the last'mentioned solvent in forming said dewaxing solution.v

3. In the art of using normally gaseous selec-f sure in a-disintegrating zone to produce forcibly disintegrated wax particles, thereby suddenly vevaporating portions of the solvent to quicklychill and precipitate waxfractions'in a liquid solution of the oiland solvent, while suddenly expanding the evaporatingportions of the Solvent in the waxy mixture tovforcibly disintegrate the Wax, transmittinga mixture of the disinte-v grated wax and oil solution into asettling chamber, discharging a stream-of de waxed oil solution from an upper portion of said settling chamber,A discharging a stream ofwax withportions of the oilsolution from a. lower portion of said settlingl chamber-to a counterflow deoiling system, transmitting arising stream of liqueed normally gaseous solvent through a descending stream of wax in said deoiling` system, dividing the rising. and descending streams into layers of diierent specic gravitiescontacting with eachother at different elevations in said deoiling system, causing the counterflowing streams of wax and'solvent to flow in intersecting paths while moving vfrom rone of said elevations to another, so as toforcibly scrub oil solution from the wax, discharging'deoiled wax from a lower portion of said deoiling system, discharging a stream of lthe used solvent with its dissolved o-il solution from an upper portion of said `deoiling' system while diverting the last mentioned stream from the contents of said settling chamber, and transmit-y ting said last mentioned streamof liqueed normally gaseous solvent and dissolved oil solution Ato said wax-containing oil, so as to recycle thev dissolved oil from said deoiling system and at the same time utilize the last mentioned solvent in forming said dewa-xing solution.

EDDIE M'. DONS. osWALD G. MAURO. ,i 

